Incident
Shortly after touchdown at Memphis, Tennessee, the flight crew in the cockpit felt a severe vibration. Suspecting the right main gear as the source, they requested maintenance personnel to inspect it. No anomalies were found. The flight then continued to Pittsburgh, Pennsylvania. Shortly after touchdown in Pittsburgh, the left main gear collapsed.
Investigation
Post-incident examination of the left main gear revealed that two spacers in the torque link assembly had been improperly installed. The investigation further determined that during reinstallation of the torque links and shimmy damper at the last maintenance check, the two spacers were installed in reverse of their normal positions.
According to aircraft manufacturer Fokker, reversal of the two spacers would result in undamped free play between the upper and lower torque link, leading to oscillations in the lateral mode of the landing gear. A review of USAir's aircraft maintenance manual, supplied by Fokker, revealed that the two spacers that were incorrectly installed on the incident airplane were not described by dimensions or verbiage.